Various instruments are known for the introduction of multi-component, especially three-component, intervertebral prostheses, which consist of two prosthesis plates, each of which is joined to a vertebral body, and a prosthesis core arranged between them.
A surgical instrument for the introduction of intervertebral prostheses is known from EP 0 333 990 A2 which consists of expanding tongs that have a holder for a prosthesis plate on the front end on each jaw. The two prosthesis plates can be first made to come very close to the expanding tongs in order to introduce them into the space between the neighboring vertebrae. Then the expanding tongs are spread out in order to be able to introduce the prosthesis core between the prosthesis plates.
DE 299 19 078 U1 discloses a surgical instrument for the introduction of intervertebral implants, which has two guide tracks that are supported pivotably at the back end, and each of which has a holding device for a prosthesis plate on their free end. A longitudinal guide for the prosthesis core is arranged between the two arms. First the two prosthesis plates are introduced into the intervertebral space in the closed position, and then the two prosthesis holders are spread apart whereby, at the same time, the prosthesis core is pushed to the distal end of the instrument until it reaches the desired end position between the prosthesis plates.
DE 102 25 703 A1 discloses an instrument for the introduction of an intervertebral prosthesis which has two prosthesis holders for a pair of prosthesis plates, the holders being joined through a parallel guide and can be separated from one another, where all parts joining the two prosthesis holders are arranged outside a middle entry opening running in the longitudinal direction of the instrument, the width of which corresponds at least to the transverse measurements of the prosthesis core to be introduced between the prosthesis plates and to the prosthesis core holder provided for this. Again, first the two prosthesis plates are introduced with the aid of the instrument and then the prosthesis plates are spread apart and the prosthesis core is introduced.
On the surfaces facing each other, the prosthesis plates have concave recesses between which the prosthesis core is set, which has similarly-formed convex protrusions. The bowed surfaces of the prosthesis plates and the prosthesis core can slide on one another within certain limits and thus permit tilting and rotation of the upper prosthesis plate with respect to the lower one, as a result of which the mobility of the spinal column section in which the intervertebral prosthesis is introduced, is ensured.
Therefore, in order to be able to introduce the prosthesis core between the two prosthesis plates, the prosthesis plates have to be spread apart relatively far so that the convex protrusions of the prosthesis core are able to slide in over the edge of the concave recesses in the prosthesis plates. Such a large spreading of the intervertebral space should, however, be avoided as much as possible in order to be able to exclude damage to the spinal column and to the vertebrae. Furthermore, the prosthesis core is usually introduced in such a way that the intervertebral space is not completely spread apart, in order to be able to introduce the prosthesis core without any expenditure of force, but that the prosthesis core is driven into a smaller intermediate space between the prosthesis plates, in which case the intervertebral space is spread especially widely only in the instant in which the convex protrusions of the prosthesis core slide over the edge of the concave recesses in the prosthesis plates. However, in this case, the prosthesis core is exposed to large loads since the force that spreads the intervertebral space acts on it so that the surface of the prosthesis core can become damaged.